1. Field of the Invention
This invention relates to a pointer detection apparatus and a pointer detection method, and more particularly to a pointer detection apparatus and a pointer detection method wherein a plurality of pointers can be detected at a high speed.
2. Description of the Related Art
Conventionally, for the detection of the position of a pointer used with a touch panel or a like apparatus, various sensor systems have been proposed, such as a resistive film system, an electrostatic coupling system and an electrostatic capacitive system. In recent years, a pointer detection apparatus of the electrostatic coupling system type has been vigorously developed.
Electrostatic coupling systems are divided into two types including a surface capacitive type and a projected capacitive type. An electrostatic coupling system of the surface capacitive type is applied, for example, in an ATM (Automated Teller Machine), and that of the projected capacitive type is applied, for example, in a mobile telephone set. In both types, a variation of the electrostatic coupling state between a sensor electrode and a pointer such as a finger or an electrostatic pen is detected in order to detect the position of the pointer.
A pointer detection apparatus of the projected capacitive electrostatic coupling system includes an electrode formed in a predetermined pattern, for example, on a transparent substrate or a transparent film. The apparatus detects a variation of the electrostatic coupling state between a pointer and the electrode when the pointer approaches the electrode. For a pointer detection apparatus of this type, various techniques for optimizing the configuration have been proposed and are disclosed, for example, in Japanese Patent Laid-Open Nos. 2003-22158, Hei 9-222947, and Hei 10-161795 (referred to as Patent Document 1, 2 and 3, respectively, hereinafter). In particular, Patent Document 1 discloses a code division multiplexing system which uses an orthogonal spread code. Patent Document 2 discloses a coordinate inputting apparatus which uses a pseudo-random signal. Patent Document 3 discloses a pen for use with an electrostatic capacitive coordinate apparatus.
A pointer detection apparatus of the type called cross point electrostatic coupling system has been developed from the projected capacitive type electrostatic coupling system. Here, operation of a pointer detection apparatus of the cross point electrostatic coupling system is described briefly with reference to the accompanying drawings. FIG. 75A shows a general configuration of a sensor section and associated elements of a pointer detection apparatus of the cross point electrostatic coupling system, and FIG. 75B illustrates an output signal waveform of the pointer detection apparatus.
Referring to FIGS. 75A and 75B, a sensor section 900 includes a transmission conductor array 901 formed from a plurality of transmission conductors 902, and a reception conductor array 903 formed from a plurality of reception conductors 904. An insulating film is formed between the transmission conductor array 901 and the reception conductor array 903. The transmission conductors 902 have a predetermined shape and extend in a predetermined direction, in FIG. 75A, in the direction indicated by an arrow mark X and are disposed in parallel to, and spaced apart by a predetermined distance from, each other. The reception conductors 904 have a predetermined shape and extend in a direction crossing the extension direction of the transmission conductors 902, that is, in the direction indicated by an arrow mark Y in FIG. 75A. The reception conductors 904 are disposed in parallel to, and spaced apart by a predetermined distance from, each other.
In a pointer detection apparatus which uses the sensor section 900 having the configuration described above, for example, a predetermined signal is supplied to a predetermined one of the transmission conductors 902. A variation of current flowing to a cross point between the predetermined transmission conductor 902, to which the predetermined signal is supplied, and a reception conductor 904 is detected at each of all cross points of the predetermined transmission conductor 902 and the reception conductors 904. Here, at a position of the sensor section 900 at which a pointer 910 such as a finger is placed, part of current flowing to the transmission conductor 902 is shunted through the pointer 910 and this changes the current flowing into the reception conductor 904. Therefore, the position of the pointer 910 can be detected by detecting a cross point between the transmission conductor 902, to which the signal is supplied, and the reception conductor 904, to which a varying amount of current flows into. Further, with a pointer detection apparatus of the cross point electrostatic coupling system, simultaneous detection of a plurality of pointers is possible because the current variation is detected for each of a plurality of cross points formed on the sensor section 900.
The principle of position detection of the cross point electrostatic coupling system is described more particularly. A case is considered here where a predetermined signal is supplied to the transmission conductor Y6 and a pointing position of the pointer 910 such as, for example, a finger on the transmission conductor Y6 is detected as seen in FIG. 75A. First, in the state where a signal is supplied to the transmission conductor Y6, the difference between currents flowing to the reception conductors X1 and X2 is detected by means of a differential amplifier 905. Then, after a predetermined interval of time, the reception conductors to be connected to the differential amplifier 905 are switched to the reception conductors X2 and X3, and the difference between currents flowing through the reception conductors X2 and X3 is detected. This operation is repeated up to the reception conductor XM.
Then, a level variation of an output signal of the differential amplifier 905 at the position of each of the cross points between the transmission conductor Y6 and the reception conductors is determined. FIG. 75B illustrates a characteristic of the level variation. Referring to FIG. 75B, the axis of abscissa of the illustrated characteristic represents detection signals output from the reception conductors X1 to XM when they are temporally successively selected and connected to the differential amplifier 905. It is to be noted that a characteristic indicated by a broken line curve in FIG. 75B represents a level variation of the signal actually output from the differential amplifier 905 and another characteristic indicated by a solid line curve represents a variation of the integration value of the output signal of the differential amplifier 905.
Since the pointer or finger 910 is placed in proximity to the cross points between the transmission conductor Y6 and the reception conductors X5 and XM-5, current flowing in the proximity of these cross points varies. Therefore, as seen in FIG. 75B, the output signal of the differential amplifier 905 varies at positions corresponding to positions in proximity to the cross points between the transmission conductor Y6 and the reception conductors X5 and XM-5, and the integration value of the output signal varies. The position of the pointer 910 can be detected based on the variation of the integration value. In the conventional pointer detection apparatus, such detection as described above is carried out while successively switching the transmission conductors to be used for the detection one by one.